US20130272466A1 - CRDM Divert Valve - Google Patents
CRDM Divert Valve Download PDFInfo
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- US20130272466A1 US20130272466A1 US13/528,217 US201213528217A US2013272466A1 US 20130272466 A1 US20130272466 A1 US 20130272466A1 US 201213528217 A US201213528217 A US 201213528217A US 2013272466 A1 US2013272466 A1 US 2013272466A1
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- coolant
- valve
- piston
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C7/00—Control of nuclear reaction
- G21C7/06—Control of nuclear reaction by application of neutron-absorbing material, i.e. material with absorption cross-section very much in excess of reflection cross-section
- G21C7/08—Control of nuclear reaction by application of neutron-absorbing material, i.e. material with absorption cross-section very much in excess of reflection cross-section by displacement of solid control elements, e.g. control rods
- G21C7/12—Means for moving control elements to desired position
- G21C7/16—Hydraulic or pneumatic drive
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
Definitions
- the following relates to the nuclear power reactor arts, nuclear reaction control apparatus arts, control rod assembly arts, and related arts.
- Pressurized water reactors traditionally utilize neutron-absorbing control rods that are moved into or out of the nuclear reactor core in order to control the reactivity.
- the control rods are operated by control rod drive mechanisms (CRDMs) that are mounted on the reactor vessel head. Penetrations in the head allow connecting rods from the control rod cluster to extend outside of the reactor vessel and connect to the CRDMs.
- CRDMs use magnets to latch the rods to the roller nut or mag jack assemblies in the CRDMs to pull the control rod clusters out of the core.
- the CRDMs are located inside the reactor vessel. See, e.g. U.S. Pub. No. 2010-0316177 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety, and U.S. Pub. No. 2011-0222640 A1 published Sep. 15, 2011 which is incorporated herein by reference in its entirety.
- the connecting rods are contemplated to be latched to the CRDM assembly by a hydraulic actuating mechanism that relies on hydraulic pressure to prevent the rods from dropping free from the CRDMs.
- a hydraulic actuating mechanism is biased to a released or disengaged state and hydraulic pressure is supplied to the hydraulic actuating mechanism to maintain the actuating mechanism in an engaged state during normal operation of the reactor.
- This provides failsafe operation as loss of hydraulic power (either intentionally or due to some hydraulic system malfunction) would result in a SCRAM.
- a valve for controlling flow of coolant to a hydraulic latching mechanism of an internal control rod drive mechanism (CRDM) disposed inside a nuclear reactor comprises a valve body having an inlet for receiving coolant, an outlet connectable to a hydraulic latching mechanism for supplying coolant thereto, and a dump port for dumping backflow coolant, a valve member movable within the valve body between a first position restricting flow between the outlet and the dump port such that coolant entering the valve body through the inlet exits the valve body through the outlet, and a second position whereat the dump port is in fluid communication with the outlet such that at least a portion of any backflow coolant flowing back into the valve body via the outlet exits the valve body via the dump port, a biasing element positioned to bias the valve member towards the second position, wherein coolant flowing into the valve body via the inlet acts on the valve member to urge the valve member towards the first position against the biasing element.
- CRDM internal control rod drive mechanism
- a nuclear reactor comprises a nuclear reactor core comprising fissile material, a pressure vessel containing the nuclear reactor core immersed in primary coolant disposed in the pressure vessel, and a valve mounted to the pressure vessel for controlling flow of coolant to a CRDM hydraulic latching mechanism.
- the valve comprises a valve body having a coolant inlet for receiving coolant from a coolant source, a coolant outlet connectable to a hydraulic latching mechanism for supplying coolant thereto, and a dump port for dumping coolant backflow, a valve member movable within the valve body between a first position restricting flow between the coolant outlet and the dump port such that coolant entering the valve body through the coolant inlet exits the valve body through the coolant outlet, and a second position whereat the dump port is in fluid communication with the coolant outlet such that at least a portion of any backflow fluid flowing back into the valve body via the coolant outlet exits the valve body via the dump port a biasing element positioned to bias the valve member towards the second position.
- the coolant flowing into the valve body via the coolant inlet acts on the valve member to urge the valve member towards the first position against the biasing element.
- a valve comprises a valve body having a coolant outlet, a coolant inlet, a biasing element, and a flange configured to mount the valve on a pressure vessel of a nuclear reactor with the valve body including the coolant outlet disposed inside the pressure vessel and the coolant inlet and the biasing element disposed outside the pressure vessel, and a divert assembly disposed in or with the valve body and configured to be held in a flow position by coolant flow passing through the valve from the coolant inlet to the coolant outlet and biased by the biasing element toward a divert position that diverts the coolant outlet to discharge into the pressure vessel upon removal of the coolant flow.
- the invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations.
- the drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention.
- FIG. 1 is a schematic diagram of an exemplary reactor in accordance with the disclosure.
- FIG. 2 is a perspective cutaway view of an exemplary flow divert valve in accordance with the disclosure.
- FIG. 3 is an enlarged portion of FIG. 2 showing the exemplary flow divert valve in a first position.
- FIG. 4 is similar to FIG. 3 but illustrates the flow divert valve in a second position.
- the coolant from the CRDM can instead be dumped directly into the pressure vessel, e.g. into the downcomer region.
- this might seem to be problematic since the pressure vessel is at elevated pressure, which indeed may be increasing in an uncontrolled manner in the event of a reactor malfunction leading to a SCRAM.
- the hydraulic latching cylinder of the internal CRDM is immersed in primary coolant contained in the pressure vessel, the pressure inside the cylinder is always higher than the pressure in the pressure vessel because of the weight supported by the hydraulic cylinder.
- the working fluid in the hydraulic latching cylinders is typically taken from the reactor coolant inventory and purification system (RCI) system, and so dumping it into the pressure vessel does not introduce any coolant contamination issues.
- the hydraulic fluid supply line used to pressurize the cylinder can be modified to dump water from the cylinder into the pressure vessel when the hydraulic pressure is turned off.
- the disclosed approach does not add any additional external piping for discharging the cylinder (removing a potential LOCA source) and provides passive discharge of the cylinder without the use of dump valves (removing another potential failure mechanism).
- the illustrative nuclear reactor is of the pressurized water reactor (PWR) variety, and includes a pressure vessel 2 containing a reactor core 3 comprising fissile material (e.g., 235 U) immersed in primary coolant water.
- PWR pressurized water reactor
- the illustrative pressure vessel 2 is generally cylindrical, and a generally cylindrical central riser 4 disposed coaxially inside the pressure vessel 2 defines a coolant circulation path in which primary coolant heated by the reactor core 3 flows upward through the central riser 4 , exits the top of the central riser 4 and flows downward back to the core 3 through a downcomer annulus 5 defined between the pressure vessel 2 and the central riser 4 .
- the primary coolant in the pressure vessel 2 is maintained in a subcooled state by pressure provided by an internal pressurizer 6 at the top of the pressure vessel 2 defined by a baffle plate 7 (or, alternatively, the pressure vessel can be connected with an external pressurizer via suitable piping.)
- an internal pressurizer 6 at the top of the pressure vessel 2 defined by a baffle plate 7 (or, alternatively, the pressure vessel can be connected with an external pressurizer via suitable piping.)
- the reactor 1 is merely illustrative of one type of reactor, and that the flow divert valve of the present disclosure can be used with a wide variety of reactors.
- one type of internal control rod drive mechanism utilizes hydraulic pressure to maintain latching force on the control rod drive connecting rods.
- FIG. 1 one such CRDM 8 is shown disposed inside the volume enclosed by the central riser 4 .
- the CRDM 8 operates on a control rod assembly including a connecting rod 9 terminating in a spider 10 that supports an assembly of neutron-absorbing control rods 11 .
- the CRDM 8 includes a motor/leadscrew assembly (not shown) for raising/lowering the control rod assembly 9 , 10 , 11 such that the control rods 11 are raised from the core 3 or lowered into the core 3 .
- the CRDM receives hydraulic pressure from a hydraulic trip divert valve 12 that is fed from a pressurized fluid source 14 , such as the RCI 14 .
- a pressurized fluid source 14 such as the RCI 14 .
- the hydraulic pressure is supplied to a hydraulic latching cylinder 16 of the CRDM 8 .
- the pressure raises a piston of the hydraulic cylinder 16 that in turn lifts a cam assembly 17 that causes a latch 18 to secure to the upper end of the connecting rod 9 .
- the cam assembly 17 includes long vertical arms that are coextensive with the travel of the latch 18 during raising/lowering of the control rod assembly 9 , 10 , 11 , and cam bars of the cam assembly 17 drive the vertical arms generally inward to engage the latch 18 when the cylinder 16 is pressurized.
- CRDM 8 /control rod assembly 9 , 10 , 11 are diagrammatic and are not to scale. Also, only one CRDM 8 /control rod assembly 9 , 10 , 11 is shown—there is an array of such CRDM/control rod assemblies provided, typically one per fuel assembly of the reactor core 3 ).
- a differential pressure between the latch cylinder 16 and ambient conditions in the reactor that is, the pressure of the coolant inside the pressure vessel 2
- the trip is not instantaneous, however.
- the hydraulic trip divert valve 12 is shown in FIG. 1 mounted to a vessel penetration of the pressure vessel 2 and extends into the downcomer annulus 5 .
- the divert valve 12 receives pressurized fluid from the RCI 14 . (Because of this, any leakage of the hydraulic fluid from the cylinder 16 is not problematic since it is purified reactor coolant). Fluid received by the divert valve 12 is directed to one or more hydraulic latching cylinders 16 of one or more CRDM devices 8 .
- the divert valve 12 provides an internal valve that, upon actuation, allows water in the CRDM latching cylinders 16 and associated tubing to drain back into the downcomer annulus 5 of the reactor pressure vessel 2 . This configuration eliminates the external piping and the dump valve, and therefore, eliminates the possibility of a LOCA from that piping and the possibility of a dump valve actuation failure.
- FIG. 2 a cross-sectional view taken through a longitudinal axis of an exemplary divert valve 12 is shown.
- the illustrated exemplary divert valve 12 utilizes the flow received from the RCI 14 to maintain the valve in a position that passes that flow into a pipe that leads to the CRDM latching cylinders 16 . If the flow from the high pressure source 14 is interrupted for any reason (e.g., an unintentional blockage or an intentional automatic or manual shutoff of the hydraulic flow to initiate a SCRAM) then a spring outside of the reactor pressure boundary shifts the valve to a second position where flow received back from the CRDM latching cylinders would drain into a reactor vessel downcomer 5 .
- any reason e.g., an unintentional blockage or an intentional automatic or manual shutoff of the hydraulic flow to initiate a SCRAM
- the divert valve 12 generally includes a valve body 20 having an axially extending central bore 24 defining a passageway between an inlet, hereinafter referred to as a high pressure inlet 28 , for receiving high pressure fluid, such as coolant, from a high pressure fluid source, and an outlet, hereinafter referred to as high pressure outlet 32 , connectable to a hydraulic latching mechanism for supplying the pressurized fluid thereto.
- the fluid may typically be a coolant such as the type commonly used in nuclear reactors, but other types of fluid can be used.
- a plurality of dump ports 36 open to an external surface of the valve body 20 and, as will be described, allow fluid to dump directly to a downcomer 5 of the reactor vessel 2 during a reactor shutdown.
- An attachment or mounting flange 38 is provided for bolting or otherwise securing the valve 12 to a pressure vessel such that the high pressure outlet 32 is disposed within the pressure vessel and the high pressure inlet 28 is disposed outside the pressure vessel. It should be appreciated that other mounting configurations are possible, and that in some instances both the high pressure inlet 28 and the high pressure outlet 32 may be disposed within the pressure vessel.
- a valve member in the form of a divert piston 40 supported within the central bore 24 of the valve body 20 is a valve member in the form of a divert piston 40 .
- Divert piston 40 is supported for reciprocating movement within the central bore 24 and is movable between a first position and a second position, as will be described below.
- the piston 40 includes a rod portion 42 that is supported within the central bore 24 by a rod support member 44 .
- the rod support member 44 has at its axially inner end a radially outwardly extending flange 48 that engages an inner surface of the central bore 24 .
- the flange 48 has a plurality of flow passages 50 that allow the flow of fluid between the high pressure fluid inlet 28 and the high pressure fluid outlet 32 when the piston 40 is in the first position. Fluid flowing through flow passages 50 enters a central cavity 54 in the piston 40 via radial ports 58 in a reduced diameter portion 59 of the piston 40 , then flows to high pressure outlet 32 . It should be understood that the flow of high pressure fluid through the valve body in this manner acts to maintain the piston 40 in the first position shown in FIG. 3 .
- rod portion 42 protrudes from the valve body 20 and has a spring flange 62 adapted to engage a spring 68 or other biasing element.
- Spring 68 is interposed between said spring flange 62 and a base portion 70 of the rod support member 44 such that the piston 40 and rod portion 42 of the valve member are biased towards the second position shown in FIG. 4 , as will be described below.
- rod support member 44 valve member including piston 40 and rod portion 42 , and the spring 68 can be inserted into the central bore 24 of the valve body 20 as a unit.
- these components can be part of a valve member assembly that can be assembled outside of the valve body 20 , and can inserted therein and bolted or otherwise secured to a base flange 72 of the valve body 20 .
- the piston 40 and/or spring 68 etc. can be easily replaced or swapped out without removal of the valve body 20 from its position within a pressure vessel or the like.
- high pressure fluid is supplied to the high pressure inlet 28 .
- Fluid flows into the central bore of the valve body 20 in the annular space between the rod support member 44 and the valve body 20 .
- the fluid passing through the flow passages 50 of the flange 48 acts upon the piston 40 , forcing the piston 40 to the position shown in FIG. 3 .
- the spring 68 is compressed between spring flange 62 and the base portion 70 of the rod support member 44 .
- the radial ports 58 in the reduced diameter portion of the piston 40 are revealed, allowing the high pressure fluid flowing through the central bore 24 from the high pressure inlet 28 to enter the central cavity 54 of the piston 40 .
- the fluid then flows out of the valve body 20 via high pressure outlet 32 .
- the flow path of fluid flowing through the valve 12 between the high pressure inlet 28 and the high pressure outlet 32 when the piston 40 is in this first positioning is illustrated by arrows A in FIG. 3 .
- the spring 68 acts to shift the piston 40 to the second position shown in FIG. 4 . That is, upon stoppage of high pressure flow to the high pressure inlet 28 , the hydraulic forces maintaining the piston 40 in the position of FIG. 3 are generally removed. Thus, spring 68 begins to retract piston 40 to its second position, as fluid pressure backflowing into the high pressure outlet 32 from the cylinder(s) of the latching mechanism also acts on the piston 40 in a common direction with the spring 68 .
- the piston 40 shifts to the position of FIG. 4 such that the reduced diameter portion 59 of the piston 40 is received in a counterbore 78 of the rod support member 44 thereby closing radial ports 58 and axial passages 50 , and also revealing dump ports 36 .
- the direction of such flow is illustrated by arrows B in FIG. 4 .
- Suitable seals can be provided on at least one of the piston 40 , valve body 20 , and/or flange 48 for preventing leakage of backflowing fluid.
- the valve body can be approximately three inches in outside diameter and configured to bolt onto the outside of a reactor.
- the valve can be configured to penetrate the pressure vessel and can be connected to piping that transports high pressure water to the one or more CRDM latching mechanisms.
- the orifices are sized to create sufficient force to hold the piston against the back face of the valve body compressing a spring on the front face of the valve (outside of the reactor coolant).
- the full stroke of the piston can be approximately 0.9 in. Neglecting friction in the valve packing, and assuming a desired spring force, the valve will move to the full open position in less than a second in one configuration, and in less than a tenth of second in another configuration wherein the spring force is more desirous. Friction will substantially increase operating time but sufficient force should be available to operate the piston quickly.
- the preload spring can be located within the pressure boundary eliminating the need for valve packing if an external actuator is not used. It will be appreciated that the spring can influence the speed at which the valve shifts, as well as initiate movement of the valve after removal of inflow pressure.
- the flow divert valve disclosed herein automatically opens when the hydraulic pumps are de-activated to provide a short path for water to flow from the CRDM latching cylinders to the RCS inside the vessel.
- the divert valve eliminates the need for pipe to direct flow back into the vessel or to an alternative reservoir.
- the divert valve opens to allow CRDMs flow to the RCS, it also isolates the RCS from flow paths outside of the reactor, preventing significant LOCA flow in the event of a pipe break outside of the reactor vessel.
- the valve arrangement shown and described in FIGS. 1-4 utilizes hydraulic pressure received from a source, for example one or more pumps, to position the valve to direct flow to the CRDMs.
- a separate isolation valve may therefore be used to move the divert valve to the tripped position. That is, the isolation valve could be configured to block flow from the high pressure source to the high pressure inlet to initiate valve state change.
- an actuator can be mounted on the divert valve to perform this function. It can be a fail open actuator such as a linear pneumatic type that holds the valve in the normally operating position while relying on the preload spring to move the valve piston when the CRDMs are to drop the rods.
- Another alternative could utilize an actuator to force the valve into normal operating position where it would be restrained by a solenoid actuated latch. Loss of electrical power to the solenoid would release that latch allowing the spring to move the divert valve.
- the divert valve is described with illustrative reference to the CRDM 8 with a hydraulic latch (for example, as described in U.S. Pub. No. 2011-0222640 A1 published Sep. 15, 2011 which is incorporated herein by reference in its entirety). More generally, the divert valve can be used in conjunction with any type of CRDM employing a hydraulic cylinder designed to initiate a scram upon removal of hydraulic power.
- the disclosed divert valves can be used in conjunction with a CRDM that employs a separable coupling to the lead screw that is maintained in the engaged state by positive hydraulic pressure.
- the disclosed divert valve can also be used in conjunction with a dedicated shutdown rod assembly that employs a pressurized hydraulic cylinder to keep the shutdown rods withdrawn from the reactor core.
- the disclosed divert valve is suitably used in any context in which a hydraulic piston is disposed inside a pressure vessel of a nuclear reactor and is advantageously discharged of hydraulic fluid upon removal of hydraulic power.
- a hydraulic piston is disposed inside a pressure vessel of a nuclear reactor and is advantageously discharged of hydraulic fluid upon removal of hydraulic power.
- other contemplated applications include hydraulic cylinders operating other systems disposed in the pressure vessel, such as a failsafe internal valve in which loss of positive hydraulic pressure causes a piston to fall under gravity so as to close the valve.
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Abstract
Description
- The following relates to the nuclear power reactor arts, nuclear reaction control apparatus arts, control rod assembly arts, and related arts.
- Pressurized water reactors traditionally utilize neutron-absorbing control rods that are moved into or out of the nuclear reactor core in order to control the reactivity. The control rods are operated by control rod drive mechanisms (CRDMs) that are mounted on the reactor vessel head. Penetrations in the head allow connecting rods from the control rod cluster to extend outside of the reactor vessel and connect to the CRDMs. These CRDMs use magnets to latch the rods to the roller nut or mag jack assemblies in the CRDMs to pull the control rod clusters out of the core.
- In some current reactor designs, the CRDMs are located inside the reactor vessel. See, e.g. U.S. Pub. No. 2010-0316177 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety, and U.S. Pub. No. 2011-0222640 A1 published Sep. 15, 2011 which is incorporated herein by reference in its entirety. In some such “internal” CRDM designs, the connecting rods are contemplated to be latched to the CRDM assembly by a hydraulic actuating mechanism that relies on hydraulic pressure to prevent the rods from dropping free from the CRDMs. That is, a hydraulic actuating mechanism is biased to a released or disengaged state and hydraulic pressure is supplied to the hydraulic actuating mechanism to maintain the actuating mechanism in an engaged state during normal operation of the reactor. This provides failsafe operation as loss of hydraulic power (either intentionally or due to some hydraulic system malfunction) would result in a SCRAM.
- In accordance with one aspect, a valve for controlling flow of coolant to a hydraulic latching mechanism of an internal control rod drive mechanism (CRDM) disposed inside a nuclear reactor comprises a valve body having an inlet for receiving coolant, an outlet connectable to a hydraulic latching mechanism for supplying coolant thereto, and a dump port for dumping backflow coolant, a valve member movable within the valve body between a first position restricting flow between the outlet and the dump port such that coolant entering the valve body through the inlet exits the valve body through the outlet, and a second position whereat the dump port is in fluid communication with the outlet such that at least a portion of any backflow coolant flowing back into the valve body via the outlet exits the valve body via the dump port, a biasing element positioned to bias the valve member towards the second position, wherein coolant flowing into the valve body via the inlet acts on the valve member to urge the valve member towards the first position against the biasing element.
- In accordance with another aspect, a nuclear reactor comprises a nuclear reactor core comprising fissile material, a pressure vessel containing the nuclear reactor core immersed in primary coolant disposed in the pressure vessel, and a valve mounted to the pressure vessel for controlling flow of coolant to a CRDM hydraulic latching mechanism. The valve comprises a valve body having a coolant inlet for receiving coolant from a coolant source, a coolant outlet connectable to a hydraulic latching mechanism for supplying coolant thereto, and a dump port for dumping coolant backflow, a valve member movable within the valve body between a first position restricting flow between the coolant outlet and the dump port such that coolant entering the valve body through the coolant inlet exits the valve body through the coolant outlet, and a second position whereat the dump port is in fluid communication with the coolant outlet such that at least a portion of any backflow fluid flowing back into the valve body via the coolant outlet exits the valve body via the dump port a biasing element positioned to bias the valve member towards the second position. The coolant flowing into the valve body via the coolant inlet acts on the valve member to urge the valve member towards the first position against the biasing element.
- In accordance with another aspect, a valve comprises a valve body having a coolant outlet, a coolant inlet, a biasing element, and a flange configured to mount the valve on a pressure vessel of a nuclear reactor with the valve body including the coolant outlet disposed inside the pressure vessel and the coolant inlet and the biasing element disposed outside the pressure vessel, and a divert assembly disposed in or with the valve body and configured to be held in a flow position by coolant flow passing through the valve from the coolant inlet to the coolant outlet and biased by the biasing element toward a divert position that diverts the coolant outlet to discharge into the pressure vessel upon removal of the coolant flow.
- The invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention.
-
FIG. 1 is a schematic diagram of an exemplary reactor in accordance with the disclosure. -
FIG. 2 is a perspective cutaway view of an exemplary flow divert valve in accordance with the disclosure. -
FIG. 3 is an enlarged portion ofFIG. 2 showing the exemplary flow divert valve in a first position. -
FIG. 4 is similar toFIG. 3 but illustrates the flow divert valve in a second position. - When tripping a reactor that employs a CRDM with a hydraulic latch (for example, as described in U.S. Pub. No. 2011-0222640 A1 published Sep. 15, 2011 which is incorporated herein by reference in its entirety), or when release of the control rods from the hydraulic actuating mechanism is otherwise desired or warranted, the hydraulic pressure must be released and backflow must be initiated to allow water in the hydraulic latch cylinders to escape before the control rods can be released. In one approach, a separate pipe is provided to dump water from the hydraulic latch cylinder to an accumulator with sufficient free volume to accommodate the fluid. A set of valves is configured to close off the water from the supply pumps while simultaneously draining the water that is in the CRDM latching cylinders back to the reactor cooling system (RCS). This approach requires small bore piping to run from the mid-flange to the dump valve and back to the mid-flange. Since this is a safety-related operation, redundant dump valves are typically provided in case one dump valve fails. If the piping that supplies water to the latching cylinders breaks, the flow through that pipe is limited by the leakage rate past the latch cylinder seals. However, if the piping that returns the fluid to the RCS breaks, the result is a significant loss of cooling accident (LOCA).
- As disclosed herein, the coolant from the CRDM can instead be dumped directly into the pressure vessel, e.g. into the downcomer region. Intuitively, this might seem to be problematic since the pressure vessel is at elevated pressure, which indeed may be increasing in an uncontrolled manner in the event of a reactor malfunction leading to a SCRAM. However, it is recognized herein that because the hydraulic latching cylinder of the internal CRDM is immersed in primary coolant contained in the pressure vessel, the pressure inside the cylinder is always higher than the pressure in the pressure vessel because of the weight supported by the hydraulic cylinder. Thus, there is always a positive differential pressure available to drive the water out of the cylinder and into the pressure vessel. Moreover, since the hydraulic latching cylinders typically cannot be guaranteed to be fully sealed against leakage, the working fluid in the hydraulic latching cylinders is typically taken from the reactor coolant inventory and purification system (RCI) system, and so dumping it into the pressure vessel does not introduce any coolant contamination issues. As disclosed herein, the hydraulic fluid supply line used to pressurize the cylinder can be modified to dump water from the cylinder into the pressure vessel when the hydraulic pressure is turned off. Thus, the disclosed approach does not add any additional external piping for discharging the cylinder (removing a potential LOCA source) and provides passive discharge of the cylinder without the use of dump valves (removing another potential failure mechanism).
- Turning now to the drawings, and initially to
FIG. 1 , an exemplary nuclear reactor in accordance with the disclosure is illustrated and identified generally byreference numeral 1. The illustrative nuclear reactor is of the pressurized water reactor (PWR) variety, and includes apressure vessel 2 containing areactor core 3 comprising fissile material (e.g., 235U) immersed in primary coolant water. Theillustrative pressure vessel 2 is generally cylindrical, and a generally cylindricalcentral riser 4 disposed coaxially inside thepressure vessel 2 defines a coolant circulation path in which primary coolant heated by thereactor core 3 flows upward through thecentral riser 4, exits the top of thecentral riser 4 and flows downward back to thecore 3 through adowncomer annulus 5 defined between thepressure vessel 2 and thecentral riser 4. The primary coolant in thepressure vessel 2 is maintained in a subcooled state by pressure provided by aninternal pressurizer 6 at the top of thepressure vessel 2 defined by a baffle plate 7 (or, alternatively, the pressure vessel can be connected with an external pressurizer via suitable piping.) It will be appreciated that thereactor 1 is merely illustrative of one type of reactor, and that the flow divert valve of the present disclosure can be used with a wide variety of reactors. - As noted above, one type of internal control rod drive mechanism (internal CRDM) utilizes hydraulic pressure to maintain latching force on the control rod drive connecting rods. In
FIG. 1 , onesuch CRDM 8 is shown disposed inside the volume enclosed by thecentral riser 4. The CRDM 8 operates on a control rod assembly including a connectingrod 9 terminating in aspider 10 that supports an assembly of neutron-absorbingcontrol rods 11. TheCRDM 8 includes a motor/leadscrew assembly (not shown) for raising/lowering thecontrol rod assembly control rods 11 are raised from thecore 3 or lowered into thecore 3. The CRDM receives hydraulic pressure from a hydraulic tripdivert valve 12 that is fed from a pressurizedfluid source 14, such as theRCI 14. During normal operation, the hydraulic pressure is supplied to ahydraulic latching cylinder 16 of theCRDM 8. The pressure raises a piston of thehydraulic cylinder 16 that in turn lifts acam assembly 17 that causes alatch 18 to secure to the upper end of the connectingrod 9. Thecam assembly 17 includes long vertical arms that are coextensive with the travel of thelatch 18 during raising/lowering of thecontrol rod assembly cam assembly 17 drive the vertical arms generally inward to engage thelatch 18 when thecylinder 16 is pressurized. If hydraulic pressure is removed from thecylinder 16 then the piston falls under force of gravity, and thecam assembly 17 drives its vertical arms outward away from thelatch 18, which then releases the connectingrod 9 causing thecontrol rod assembly reactor core 3 under force of gravity. Further details of theCRDM 8 including thehydraulic latching cylinder 16,cam assembly 17, andlatch 18 are described in U.S. Pub. No. 2011-0222640 A1 published Sep. 15, 2011 which is incorporated herein by reference in its entirety. (Note that inFIG. 1 , thereactivity control components FIG. 1 are diagrammatic and are not to scale. Also, only oneCRDM 8/control rod assembly latch cylinder 16 and ambient conditions in the reactor (that is, the pressure of the coolant inside the pressure vessel 2) is needed to keep the piston of thelatch cylinder 16 raised so as to engage thelatch 18 to prevent dropping thecontrol rods 11 into thereactor core 3 and initiating a reactor shutdown. The trip (unlatching of the rods) is not instantaneous, however. Once pressure to the cylinder(s) is terminated, there is a finite amount of water in the latching cylinders (˜one gallon total) that must be drained before the pistons can move far enough to release the control rods. Thus, there is a delay before the control rods release as this water drains from the pistons. It should be noted that the foregoing pressure and volume values are illustrative examples for a contemplated PWR with internal pressurizer and internal CRDMS, and other pressure/volume values may be used in other designs. - The hydraulic trip divert
valve 12 is shown inFIG. 1 mounted to a vessel penetration of thepressure vessel 2 and extends into thedowncomer annulus 5. The divertvalve 12 receives pressurized fluid from theRCI 14. (Because of this, any leakage of the hydraulic fluid from thecylinder 16 is not problematic since it is purified reactor coolant). Fluid received by the divertvalve 12 is directed to one or morehydraulic latching cylinders 16 of one ormore CRDM devices 8. The divertvalve 12 provides an internal valve that, upon actuation, allows water in theCRDM latching cylinders 16 and associated tubing to drain back into thedowncomer annulus 5 of thereactor pressure vessel 2. This configuration eliminates the external piping and the dump valve, and therefore, eliminates the possibility of a LOCA from that piping and the possibility of a dump valve actuation failure. - Turning to
FIG. 2 , a cross-sectional view taken through a longitudinal axis of an exemplary divertvalve 12 is shown. The illustrated exemplary divertvalve 12 utilizes the flow received from theRCI 14 to maintain the valve in a position that passes that flow into a pipe that leads to theCRDM latching cylinders 16. If the flow from thehigh pressure source 14 is interrupted for any reason (e.g., an unintentional blockage or an intentional automatic or manual shutoff of the hydraulic flow to initiate a SCRAM) then a spring outside of the reactor pressure boundary shifts the valve to a second position where flow received back from the CRDM latching cylinders would drain into areactor vessel downcomer 5. - The divert
valve 12 generally includes avalve body 20 having an axially extendingcentral bore 24 defining a passageway between an inlet, hereinafter referred to as ahigh pressure inlet 28, for receiving high pressure fluid, such as coolant, from a high pressure fluid source, and an outlet, hereinafter referred to ashigh pressure outlet 32, connectable to a hydraulic latching mechanism for supplying the pressurized fluid thereto. As will be appreciated, the fluid may typically be a coolant such as the type commonly used in nuclear reactors, but other types of fluid can be used. A plurality ofdump ports 36 open to an external surface of thevalve body 20 and, as will be described, allow fluid to dump directly to adowncomer 5 of thereactor vessel 2 during a reactor shutdown. An attachment or mountingflange 38 is provided for bolting or otherwise securing thevalve 12 to a pressure vessel such that thehigh pressure outlet 32 is disposed within the pressure vessel and thehigh pressure inlet 28 is disposed outside the pressure vessel. It should be appreciated that other mounting configurations are possible, and that in some instances both thehigh pressure inlet 28 and thehigh pressure outlet 32 may be disposed within the pressure vessel. - With further reference to
FIGS. 3 and 4 , supported within thecentral bore 24 of thevalve body 20 is a valve member in the form of a divertpiston 40. Divertpiston 40 is supported for reciprocating movement within thecentral bore 24 and is movable between a first position and a second position, as will be described below. It will be noted that thepiston 40 includes arod portion 42 that is supported within thecentral bore 24 by arod support member 44. Therod support member 44 has at its axially inner end a radially outwardly extendingflange 48 that engages an inner surface of thecentral bore 24. Theflange 48 has a plurality offlow passages 50 that allow the flow of fluid between the highpressure fluid inlet 28 and the highpressure fluid outlet 32 when thepiston 40 is in the first position. Fluid flowing throughflow passages 50 enters acentral cavity 54 in thepiston 40 viaradial ports 58 in a reduceddiameter portion 59 of thepiston 40, then flows tohigh pressure outlet 32. It should be understood that the flow of high pressure fluid through the valve body in this manner acts to maintain thepiston 40 in the first position shown inFIG. 3 . - Returning to
FIG. 2 ,rod portion 42 protrudes from thevalve body 20 and has aspring flange 62 adapted to engage aspring 68 or other biasing element.Spring 68 is interposed between saidspring flange 62 and abase portion 70 of therod support member 44 such that thepiston 40 androd portion 42 of the valve member are biased towards the second position shown inFIG. 4 , as will be described below. - It should be appreciated that the
rod support member 44, valvemember including piston 40 androd portion 42, and thespring 68 can be inserted into thecentral bore 24 of thevalve body 20 as a unit. To this end, these components can be part of a valve member assembly that can be assembled outside of thevalve body 20, and can inserted therein and bolted or otherwise secured to abase flange 72 of thevalve body 20. Accordingly, thepiston 40 and/orspring 68 etc. can be easily replaced or swapped out without removal of thevalve body 20 from its position within a pressure vessel or the like. - In operation, high pressure fluid is supplied to the
high pressure inlet 28. Fluid flows into the central bore of thevalve body 20 in the annular space between therod support member 44 and thevalve body 20. The fluid passing through theflow passages 50 of theflange 48 acts upon thepiston 40, forcing thepiston 40 to the position shown inFIG. 3 . As thepiston 40 is moved, thespring 68 is compressed betweenspring flange 62 and thebase portion 70 of therod support member 44. As will be appreciated, whenpiston 40 is forced to the left (position shown inFIG. 3 ), theradial ports 58 in the reduced diameter portion of thepiston 40 are revealed, allowing the high pressure fluid flowing through thecentral bore 24 from thehigh pressure inlet 28 to enter thecentral cavity 54 of thepiston 40. The fluid then flows out of thevalve body 20 viahigh pressure outlet 32. The flow path of fluid flowing through thevalve 12 between thehigh pressure inlet 28 and thehigh pressure outlet 32 when thepiston 40 is in this first positioning is illustrated by arrows A inFIG. 3 . - In the first position shown in
FIG. 3 , thepiston 40 blocks flow of fluid between both thehigh pressure inlet 28 andoutlet 32, and thedump ports 36, such that any high pressure fluid entering thevalve body 20 through thehigh pressure inlet 28 is directed to thehigh pressure outlet 32. In this regard, thepiston 40 is in abutting engagement with an internal axial end face 74 of thecentral bore 24. In this position, thedump ports 36 are blocked by the radial outer surface of thepiston 40. Further sealing can be provided via sealing elements disposed in the axial mating faces of thepiston 40 and the central bore, and/or disposed at the circumferential interface of thepiston 40 andcentral bore 24. In some applications, it should be appreciated that a small amount of leakage may exit thevalve body 20 throughdump ports 36 even when the piston is in the first position. - When high pressure fluid is no longer supplied to the
high pressure inlet 28, such as during a SCRAM or other shutdown of a reactor where it is desired to release the latching mechanism(s) holding the control rods to the CRDM, thespring 68 acts to shift thepiston 40 to the second position shown inFIG. 4 . That is, upon stoppage of high pressure flow to thehigh pressure inlet 28, the hydraulic forces maintaining thepiston 40 in the position ofFIG. 3 are generally removed. Thus,spring 68 begins to retractpiston 40 to its second position, as fluid pressure backflowing into thehigh pressure outlet 32 from the cylinder(s) of the latching mechanism also acts on thepiston 40 in a common direction with thespring 68. - Accordingly, the
piston 40 shifts to the position ofFIG. 4 such that the reduceddiameter portion 59 of thepiston 40 is received in acounterbore 78 of therod support member 44 thereby closingradial ports 58 andaxial passages 50, and also revealingdump ports 36. This effectively isolates thehigh pressure inlet 28 from thehigh pressure outlet 32, and directs backflowing fluid received in thehigh pressure outlet 32 to thedump ports 36, where such fluid flows out of thevalve body 20 into the downcomer or other flow region within the pressure vessel. The direction of such flow is illustrated by arrows B inFIG. 4 . Suitable seals can be provided on at least one of thepiston 40,valve body 20, and/orflange 48 for preventing leakage of backflowing fluid. - In an illustrative embodiment, the valve body can be approximately three inches in outside diameter and configured to bolt onto the outside of a reactor. The valve can be configured to penetrate the pressure vessel and can be connected to piping that transports high pressure water to the one or more CRDM latching mechanisms. High pressure fluid received from redundant pumps, for example, enters the valve outside of the pressure vessel and flows through an annular region as described until it reaches the divert piston. There, the fluid is forced to turn and pass through one or more orifices to reach the flow path in the center of the piston, for example as seen in the valve of
FIG. 3 . The orifices are sized to create sufficient force to hold the piston against the back face of the valve body compressing a spring on the front face of the valve (outside of the reactor coolant). - If the pump flow is interrupted by a fast acting block valve, for example, the hydraulic pressure on the face of the piston is lost. The spring will accelerate the piston to the open position (
FIG. 4 ) blocking flow back to the pumps via the high pressure inlet and allowing fluid in the CRDM latching mechanisms to flow into the reactor vessel. In one exemplary configuration, the full stroke of the piston can be approximately 0.9 in. Neglecting friction in the valve packing, and assuming a desired spring force, the valve will move to the full open position in less than a second in one configuration, and in less than a tenth of second in another configuration wherein the spring force is more desirous. Friction will substantially increase operating time but sufficient force should be available to operate the piston quickly. Other than the packing at the spring end of the valve, component clearances can be large minimizing binding and friction. With proper thermal design, the preload spring can be located within the pressure boundary eliminating the need for valve packing if an external actuator is not used. It will be appreciated that the spring can influence the speed at which the valve shifts, as well as initiate movement of the valve after removal of inflow pressure. - The flow divert valve disclosed herein automatically opens when the hydraulic pumps are de-activated to provide a short path for water to flow from the CRDM latching cylinders to the RCS inside the vessel. The divert valve eliminates the need for pipe to direct flow back into the vessel or to an alternative reservoir. When the divert valve opens to allow CRDMs flow to the RCS, it also isolates the RCS from flow paths outside of the reactor, preventing significant LOCA flow in the event of a pipe break outside of the reactor vessel.
- The valve arrangement shown and described in
FIGS. 1-4 utilizes hydraulic pressure received from a source, for example one or more pumps, to position the valve to direct flow to the CRDMs. A separate isolation valve may therefore be used to move the divert valve to the tripped position. That is, the isolation valve could be configured to block flow from the high pressure source to the high pressure inlet to initiate valve state change. Alternatively, an actuator can be mounted on the divert valve to perform this function. It can be a fail open actuator such as a linear pneumatic type that holds the valve in the normally operating position while relying on the preload spring to move the valve piston when the CRDMs are to drop the rods. Another alternative could utilize an actuator to force the valve into normal operating position where it would be restrained by a solenoid actuated latch. Loss of electrical power to the solenoid would release that latch allowing the spring to move the divert valve. - The divert valve is described with illustrative reference to the
CRDM 8 with a hydraulic latch (for example, as described in U.S. Pub. No. 2011-0222640 A1 published Sep. 15, 2011 which is incorporated herein by reference in its entirety). More generally, the divert valve can be used in conjunction with any type of CRDM employing a hydraulic cylinder designed to initiate a scram upon removal of hydraulic power. For example, the disclosed divert valves can be used in conjunction with a CRDM that employs a separable coupling to the lead screw that is maintained in the engaged state by positive hydraulic pressure. The disclosed divert valve can also be used in conjunction with a dedicated shutdown rod assembly that employs a pressurized hydraulic cylinder to keep the shutdown rods withdrawn from the reactor core. See, e.g. U.S. Pub. No. 2010-0316177 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety. Still more generally, the disclosed divert valve is suitably used in any context in which a hydraulic piston is disposed inside a pressure vessel of a nuclear reactor and is advantageously discharged of hydraulic fluid upon removal of hydraulic power. In addition to the disclosed application in conjunction with an internal CRDM with hydraulic latching, other contemplated applications include hydraulic cylinders operating other systems disposed in the pressure vessel, such as a failsafe internal valve in which loss of positive hydraulic pressure causes a piston to fall under gravity so as to close the valve. - The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (20)
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/528,217 US20130272466A1 (en) | 2012-04-17 | 2012-06-20 | CRDM Divert Valve |
PCT/US2013/024818 WO2013158198A1 (en) | 2012-04-17 | 2013-02-06 | Crdm divert valve |
CN201310129556.6A CN103557346A (en) | 2012-04-17 | 2013-04-15 | Crdm divert valve |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US201261625212P | 2012-04-17 | 2012-04-17 | |
US13/528,217 US20130272466A1 (en) | 2012-04-17 | 2012-06-20 | CRDM Divert Valve |
Publications (1)
Publication Number | Publication Date |
---|---|
US20130272466A1 true US20130272466A1 (en) | 2013-10-17 |
Family
ID=49325089
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/528,217 Abandoned US20130272466A1 (en) | 2012-04-17 | 2012-06-20 | CRDM Divert Valve |
Country Status (3)
Country | Link |
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US (1) | US20130272466A1 (en) |
CN (1) | CN103557346A (en) |
WO (1) | WO2013158198A1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US9180557B1 (en) * | 2014-04-21 | 2015-11-10 | Areva Inc. | Two-piece replacement nozzle |
US11488732B2 (en) * | 2017-03-23 | 2022-11-01 | Kepco Engineering & Construction Company, Inc. | Secondary shutdown structure of nuclear reactor by using sliding doors |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN107004447B (en) * | 2014-12-31 | 2020-02-21 | 泰拉能源公司 | Automatic hydraulic pneumatic actuating device |
FR3044155B1 (en) * | 2015-11-23 | 2017-11-10 | Commissariat Energie Atomique | PASSIVE TRIP SECURITY DEVICE FOR NUCLEAR REACTOR ON ABNORMAL PRIMARY RATE DROP |
FR3044156B1 (en) * | 2015-11-23 | 2017-11-10 | Commissariat Energie Atomique | PASSIVE TRIP SECURITY DEVICE FOR NUCLEAR REACTOR ON ABNORMAL PRIMARY RATE DROP |
CN111370148B (en) * | 2018-12-25 | 2024-05-14 | 国家电投集团科学技术研究院有限公司 | Two sets of shutdown mechanisms of reactor and reactor |
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US5287829A (en) * | 1989-08-28 | 1994-02-22 | Rose Nigel E | Fluid actuators |
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US3841202A (en) * | 1972-03-20 | 1974-10-15 | Combustion Eng | Control valve and method |
US5028383A (en) * | 1990-04-16 | 1991-07-02 | General Electric Company | Nuclear reactor steam depressurization valve |
DE4041418A1 (en) * | 1990-12-21 | 1992-06-25 | Siemens Ag | ARRANGEMENT FOR PRESSURE SECURING A PRESSURE TANK |
CN1150565C (en) * | 1998-12-25 | 2004-05-19 | 东芝株式会社 | Control rod drive water pressure apparatus |
CN100386547C (en) * | 2003-08-29 | 2008-05-07 | 赵文轩 | Safety valve for nucleus |
GB2434385B (en) * | 2006-01-19 | 2010-07-14 | Schlumberger Holdings | Wellbore system and method using a flow-actuated diverter valve |
JP4958954B2 (en) * | 2009-09-16 | 2012-06-20 | 日立Geニュークリア・エナジー株式会社 | Control rod handling method and control rod handling device |
US8811562B2 (en) * | 2010-03-12 | 2014-08-19 | Babcock & Wilcox Nuclear Operations Group, Inc. | Control rod drive mechanism for nuclear reactor |
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2012
- 2012-06-20 US US13/528,217 patent/US20130272466A1/en not_active Abandoned
-
2013
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- 2013-04-15 CN CN201310129556.6A patent/CN103557346A/en active Pending
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US3779865A (en) * | 1969-10-15 | 1973-12-18 | Krupp Gmbh | Feed-through connection for a pressure vessel, especially a nuclear-reactor shell |
US3844882A (en) * | 1971-12-23 | 1974-10-29 | Combustion Eng | Lift piston assembly |
US4030972A (en) * | 1974-04-22 | 1977-06-21 | Combustion Engineering, Inc. | Fluidly driven control rod |
US4057074A (en) * | 1976-08-24 | 1977-11-08 | The United States Of America As Represented By The United States Energy Research And Development Administration | Bidirectional piston valve |
US5287829A (en) * | 1989-08-28 | 1994-02-22 | Rose Nigel E | Fluid actuators |
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US9180557B1 (en) * | 2014-04-21 | 2015-11-10 | Areva Inc. | Two-piece replacement nozzle |
US11488732B2 (en) * | 2017-03-23 | 2022-11-01 | Kepco Engineering & Construction Company, Inc. | Secondary shutdown structure of nuclear reactor by using sliding doors |
Also Published As
Publication number | Publication date |
---|---|
WO2013158198A1 (en) | 2013-10-24 |
CN103557346A (en) | 2014-02-05 |
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